The invention is based on a valve device, in particular for tank ventilation in motor vehicles.
A valve device of this kind is used to regenerate the activated charcoal in the fuel vapor retention system for fuel circuits in motor vehicles as described for example in the reference Boschxe2x80x94Technische Unterrichtung, Motormanagement Motronic [Boschxe2x80x94Technical Instruction, Engine Management Motronics], 2nd edition, August 1993, pp. 48 and 49. Fuel retention systems limit HC emissions and are equipped with an activated charcoal container to which a ventilation line leads from the fuel tank. The activated charcoal retains the fuel vapor and permits only the air to escape into the atmosphere, which simultaneously provides for a pressure compensation. In order to repeatedly regenerate the activated charcoal, another line leads from the activated charcoal container to an intake tube in which a vacuum is produced when the engine is running, which causes air to flow from the atmosphere, through the activated charcoal, and into the intake tube. As a result, the temporarily stored fuel vapor is entrained and is supplied to the combustion in the engine. The regenerating flow is metered by means of a valve device of the type mentioned at the beginning in the line to the intake tube.
The regenerating flow is an air/fuel mixture that is composed of air enriched with fuel vapor. Because its composition cannot be measured or can only be measured at a very high-cost, the regenerating flow represents a considerable impedance for the lambda closed-loop control since in addition, the specific density of fuel vapor is approximately twice as high as that of air. The valve device is therefore triggered so that the activated charcoal container is sufficiently rinsed and the lambda deviations are as minimal as possible.
The regenerating valve is closed at regular intervals so that the mixture adaptation can function independently of tank ventilation influences. The valve device is preferably embodied in the shape of a ramp.
The design of such a valve device for tank ventilation is known, for example, from DE 195 40 021 A1. The valve device is comprised of a valve housing, which has an inlet fitting for connecting to a ventilation fitting of the fuel tank or an adsorption filter or activated charcoal container connected to the tank and an outlet fitting for connecting to the intake tube, an armature is provided, which is disposed inside the valve housing, can be moved by an electromagnet, is pressed against a sealing seat by a valve spring and closes a flow connection from the inlet fitting to the outlet fitting when the electromagnet is without power, and opens this flow connection when the electromagnet is supplied with power. In order to be able to precisely meter extremely small fuel vapor quantities while at the same time having a simple design, a metering opening is provided, preferably with a V-shaped cross sectional area, and this opening is disposed between the inlet fitting and the sealing seat and can be controlled by the armature.
Another valve device of the type mentioned at the beginning has been disclosed by DE 297 17 078 U1. With this tank ventilation valve, the armature is connected to a closing body, which can continuously change a free cross-sectional area between the inlet fitting and the outlet fitting from a sealed position to a maximal position. The closing body is preferably constituted by a sealing disk that has a through opening and rests on a sealing seat of the outlet fitting. The sealing disk is pressed against the sealing seat with a slight pressure by way of a spring element so that the sealing disk rests in a sealed fashion against this seat but remains movably supported. In this connection, the spring element is guided by pins on the sealing disk on the one hand and on a screen in the inlet fitting on the other. In this embodiment, the spring element must move along with the valve stroke so that as a result of being deformed in a direction radial to its longitudinal axis, the spring element exerts undesirable lateral forces on the magnet armature support and on the sealing seat. Furthermore, the sealing disk can therefore tilt in its provided mount and sealing problems arise at the sealing seat of this tank ventilation valve.
The valve device has the advantage over the prior art that due to the construction of the spring element with a leaf spring, which is connected to both the armature and the closing body, the entire apparatus of the closing body and spring element moves along with the stroke of the armature. As a result of this, no disruptive lateral forces occur at the spring element and at the same time, manufacture tolerances of the sealing seat and closing body can be compensated for so that the sealing seat of the outlet fitting is sealed better and more reliably.
The valve device has an advantage that the spiral spring of the spring element deforms exclusively in the direction of its longitudinal axis during the stroke motion of the armature so that here, too, no lateral forces occur at the spring element which could lead to sealing problems. To this end, it is particularly advantageous to rotatably support the spring element in the valve housing so that the stroke motion of the armature produces a rotating motion of the spring element. Likewise, the spring element can be disposed in an advantageously stationary fashion in the valve housing and at the same time, the spring element is not connected to the closing body which means that the closing body can move along with the stroke motion of the armature while the spring element remains unchanged in its position.
The valve devices according to the invention are furthermore suitable for engines with gasoline direct injection since large scavenging quantities of fuel vapor can also be conveyed without trouble through the valve devices. Furthermore, the valve devices can be operated in both a continuous and pulsed fashion with high and low frequencies.
Other advantageous embodiments and improvements of the valve devices disclosed are possible by means of the measures disclosed herein after.
It is particularly advantageous that the fastening device of the closing body on the armature is guided in a housing groove in the valve housing in order to prevent the armature and the components connected to it from rotating or tilting and therefore to prevent a leak at the sealing seat.